Guess available or requires are in this case not so different.
It is not possible by today to receive directory services for a Cisco TelePresence
system directly from an LDAP source. Maybe that could be a feature request.
Btw, you can try TMS with up to three system for free. If you can do some
programming maybe you can reverse engineer what you need.
I am not aware if the communication is documented somewhere.
An other option is that you can upload a favorites file or even write a script
which reads out the existing phonebook, removes or adds entries and uploads it again
(or simply pushes out one phonebook per device during the night (which would
overwrite the users settings).
You will find more in the forum, check out
https://supportforums.cisco.com/thread/2160559
for example or search for it.
Besides that you can always think of filing a feature request.